Crash rail for a vehicle

ABSTRACT

The present invention provides a crash rail for a vehicle. The crash rail has a root portion which can be anchored to a part of the vehicle, a tip portion which is spaced apart from the root portion and which is located nearer a potential impact point of the vehicle when the root portion is anchored to the said part of the vehicle and a middle portion which extends from the root portion to the tip portion. The crash rail comprises a wall which defines a groove or a cavity in the crash rail. The groove or the cavity in the crash rail has a cross-sectional area which increases gradually from the tip portion to the root portion. The wall has a thickness which increases gradually from the tip portion to the root portion. The wall is composed of a composite material having fibers set in a resin material. The crash rail can be crushed when the vehicle impacts with another object to thereby absorb energy of the impact. During the impact the crash rail disintegrates with the resin separating from the fibers set therein. During the impact the crash rail disintegrates progressively with the tip portion disintegrating first and then the middle portion and lastly the root portion.

The present invention relates to a crash rail suitable for use in avehicle.

It is an acknowledged requirement that motor vehicles should have arigid passenger cell resistant to deformation and, at least in front andbehind the passenger cell, crash structures which on impact of thevehicle with another object deform in a controlled manner to absorb theenergy of the impact and to protect passengers located in the passengercell. These crash structures can comprise crash rails.

The present invention provides a crash rail for a vehicle comprising:

a root portion which can be anchored to a part of the vehicle;

a tip portion which is spaced apart from the root portion and which islocated nearer a potential impact point of the vehicle when the rootportion is anchored to the said part of the vehicle; and

a middle portion which extends from the root portion to the tip portion;wherein:

the crash rail comprises a wall which defines a groove or a cavity inthe crash rail;

the groove or the cavity in the crash rail has a cross-sectional areawhich increases gradually from the tip portion to the root portion;

the wall has a thickness which increases gradually from the tip portionto the root portion;

the wall is composed of a composite material having fibres set in aresin material;

the crash rail can be crushed when the vehicle impacts with anotherobject to thereby absorb energy of the impact;

during the impact the crash rail disintegrates with the resin separatingfrom the fibres set therein; and

during the impact the crash rail disintegrates progressively with thetip portion disintegrating first and then the middle portion and lastlythe root portion.

The present invention also provides a wheeled motor vehicle comprisingthe crash rail described above.

Preferred embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings inwhich:

FIG. 1 is a schematic view of a front of a vehicle stripped away toreveal two crash rails according to a first embodiment of the presentinvention;

FIG. 2 is a perspective view of one of the crash rails shown in FIG. 1;

FIG. 3 is a cross-section through the crash rail of FIG. 2;

FIG. 4 is an exploded perspective view showing the arrangement of fibresin a tip portion of a wall of the crash rail of FIGS. 2 and 3;

FIG. 5 is an exploded perspective view showing the arrangement of fibresin a root portion of a wall of the crash rail of FIGS. 2 and 3;

FIG. 6 is a schematic view illustrating the arrangement of longitudinalfibres in the core of a wall of the crash rail according to the presentinvention;

FIG. 7 is a perspective view of a second embodiment of crash railaccording to the present invention;

FIG. 8 is a perspective view of a third embodiment of crash railaccording to the present invention;

FIG. 9 is a perspective view of a fourth embodiment of crash railaccording to the present invention; and

FIG. 10 is a perspective view of the crash rail of FIG. 9 in analternative configuration.

Referring first to FIG. 1, there can be s seen a passenger cell 10 of amotor vehicle having a front bulkhead 11. Attached to the bulkhead 11and extending forward of the bulkhead 11 are two crash rails 20. Thesecrash rails 20 extend one either side of an engine (not shown) of themotor vehicle, through the vehicle front wings (not shown). Theforwardmost ends of the crash rails 20 are connected together by abumper (not shown) of the vehicle, to which they are both attached.

Each crash rail 20 is composed of a composite material comprising fibresarranged in a resin matrix. The composite material is described indetail below. As can be seen at 21 in FIG. 2, each crash rail 20 has ahollow square or rectangular transverse cross-section. Thecross-sectional area of each crash rail 20 tapers linearly from alargest cross-section at a root portion 22 of the crash rail 20 adjacentthe bulkhead 11 to a smallest cross-section at the forwardmost tipportion 21 of the crash rail 20. Furthermore, as is illustrated in FIG.3, the wall thickness δ of a crash rail 20 tapers linearly from alargest wall thickness δ at the root portion 22 to a smallest wallthickness δ at the tip portion 21.

Typically in a passenger motor vehicle each of the crash rails 20 willbe 600 to 700 mm long and the wall thickness δ will decrease from amaximum of 6 mm in the root portion 22 to a minimum of 2.5 mm in the tipportion 21.

Referring now to FIGS. 4 and 5, there can be seen respectively tip androot portions of a wall of a crash rail 20. The wall is composed of acomposite material comprising a plurality of layers 25, 26, 27, 28 offibres arranged in a resin matrix. Layers 26, 27, 28 of fibrous mattingare provided near the exterior surfaces of the crash rail 20 and layers25 of glass fibres in the centre. The longitudinal fibres in layers 25are all orientated to run lengthwise along the tapering walls of thecrash rail 20, each extending from the root portion 22 towards the tipportion 21. The longitudinal fibres in layers 25 in the core are ofdifferent lengths and are arranged in bundles (tows) so as to formlaminae of different lengths. All of the longitudinal fibres 25 runforwardly from the root portion 22 of the crash rail 20, but only thelongest run all the way to the tip portion 21. The remainder of thelongitudinal fibres 25 stop short at defined intervals so as to form agraduated arrangement of laminae which provides the requisite taper inthe crash rail 20. This arrangement is best illustrated in FIG. 6.

The fibrous matting comprises fibres 26, 27, 28 which areomnidirectional in nature and which extend along the entire length ofthe crash rail 20.

In the preferred embodiment, the fibrous matting layers 26, 27, 28comprises carbon fibres and the layers 25 in the core comprises glassfibres. The crash rail 20 can be formed by hand laying the fibrousmatting and the longitudinally extending fibres 25 in a mould tool andthen injecting a polyester resin (e.g. with vacuum assistance) into themould tool when closed. Epoxy or polyvinyl resins can be used.

The configuration of the fibres in the crash rail 20 gives the crashrail 20 material properties which vary along its length. At the tipportion 21 of the crash rail 20, the presence of the omnidirectionalfibre matting dominates the material characteristics as can best be seenin FIG. 4. Conversely, the omnidirectional fibrous matting has a lesserinfluence on the characteristics of the material in the root portion 22of the crash rail 20 as can best be seen in FIG. 5. This distribution offibres is significant in terms of the way in which the crash rail 20performs.

The crash rails 20 are designed to crush in a controlled manner in acrash. Metal crash rails known in the art have a high tendency to buckleon impact, but the crash rails 20 of the present invention are designednot to buckle. Instead, during an impact the crash rails 20 graduallydisintegrate from their tip portions 21 progressing towards the rootportions 22 as the resin matrix of each rail 20 detaches from the fibres25, 26, 27, 28 it encases. The crash rails 20 are designed such that thematerial of each rail 20 starts to disintegrate well before the crashrails 20 buckle under the applied d forces, even when the applied forcesdo not act longitudinally along the crash rails 20 but apply bendingmoments to them. The tapering cross-sectional area of the crash rails 20and the tapering wall thickness δ help the crash rails 20 to resistbending.

The crash rails 20 are designed so that the static strength of the railsincreases towards the root 22, typically from 200 MPa near the tip 21 ofthe crash rail 20 to 270 MPa near the root 22 (due to the varyingmaterial properties along the crash rail 20 due to the fibrereinforcement configuration). When the rails 20 are being crushed in animpact the dynamic strength of the material (i.e. the strength of thatpart of the material being crushed/disintegrating) is considerably lessthan the static strength. The dynamic strength also varies along thecrash rail, typically from 80 MPa at the tip 21 to 40 MPa at the root22, due to the varying material characteristics along the crash rail 20occasioned by the distribution of fibres 25, 26, 27, 28. It is importantto have decreasing material crush strength towards the root 22 in orderto achieve a fairly constant crush force along the length of the crashrail 20. The crush force is the product of the crush resistance and thecross-sectional area of material. Since the cross-sectional area ofmaterial to be crushed increase towards the root 22, the crushresistance must be decreased in order to ensure a reasonably consistentcrush force.

The energy dissipation of the composite material during crushingcompares favourably with steel. Steel has a typical value of 5 J/g(energy dissipated per unit mass), whilst the composite material has atypical value of 35 J/g. The invention permits the use of 6 Kg ofcomposite material in place of 35 Kg of steel.

The crash rails 20 illustrated in FIG. 1 are flared outwardly slightly(i.e. the centres of the root portion 22 of the crash rails 20 arecloser to one another than the centres of the tip portions 21). Thishelps the crash rails 20 deal with offset impacts.

A second embodiment of crash rail 30 according to the present inventionis shown in FIG. 7. The crash rail 30 tapers in the same way as thecrash rail 20 and has a wall thickness which increases towards the rootportion 32 which is attached to the bulkhead 11. However, whilst thecrash rail 20 is formed as a single integer the crash rail 30 is formedfrom two component parts 30A and 30B which have flanges (e.g. 33) andwhich are joined together by adhesive along the flanges. The fibres inthe crash rail 30 are laid out in the same fashion as those describedwith crash rail 20. The crash rail 30 functions in the same way as thecrash rail 20, but crash rail 30 is easier to manufacture.

A third embodiment of crash rail 40 according to the present inventionis shown in FIG. 8. In this embodiment the crash rail 40 compriseseffectively two crash rails 30 joined together. The crash rail 40 isformed of two matching parts 40A and 40B. The parts 40A and 40B haveflanges (e.g. 43, 44, 45) which can abut each other and which are joinedtogether by an adhesive. When the two parts 40A and 40B are adheredtogether they define two parallel identical hollow cross-sectionaltapering rail portions 46, 47. Each rail portion 46, 47 has across-section and a wall thickness which increases towards the rootportion 42 thereof, in the same manner as the crash rails 20 and 30. Thefibres in each rail portion 46, 47 are laid out in the same fashion asthose described in the crash rails 20 and 30. The crash rail 40 willoperate during an impact in the same way as crash rails 20 and 30, andwill operate as a pair of parallel spaced apart crash rails 30.

A further embodiment of crash rail 50 according to the present inventionis shown in FIG. 9. The crash rail 50 comprises a corrugated sheetequivalent to one half (e.g. 40B) of the crash rail 40. Attached toflanges 53, 54, 55 of the crash rail 50 is a flat sheet 58. The sheet 58is attached by an adhesive. The flat sheet 58 and the corrugated sheetdefine two hollow tapering cavity sections 56, 57. The cross-sectionalareas of these sections 56, 57 taper linearly along the length of thecrash rail 50 from areas of greatest cross-section at the root portions52 to areas of smallest cross-section at the tip portions 51. The wallthickness of the corrugated sheet will increase linearly towards theroot portion 52 of the rail 50.

During a crash the material of the corrugated sheet will disintegrate aswith the crash rails 20, 30 and 40. However, the flat sheet 58 will notdisintegrate, but will peel away from the corrugated sheet. The peelingwill be facilitated by a suitable choice of adhesive bonding between theflat sheet 58 and the corrugated sheet.

Whilst above the cross-sections of the cavities in the crash rails 20,30, 40, 50 are either square or rectangular, the cross-sections could beof any convenient polygonal shape and could be curved in nature. Forexample, the crash rails 20, 30, 40 could be of circular sections andcrash rail 50 of semi-circular section.

The flat sheet 58 of crash rail 50, up until peeling away, acts as astabilising panel and helps the corrugated sheet resist torsional loads.The flat sheet 58 could form a panel of an engine bay of a vehicle. Theflat sheet 58 will typically be a glass fibre panel. The flat sheet 58could itself be corrugated, with corrugations smaller than those of thecorrugated panel. The corrugations of the flat sheet 58 would preventcracks propagating throughout the adhesive layer between the sheet 58and the corrugated sheet on impact.

The crash rails 20, 30, 40, 50 could be mounted to the bulkhead 11 byslotting the root ends 22, 32, 42, 52 into matching slots in castuprights attached to or integral with the bulkhead 11. A suitablearrangement for crash rail 50 is illustrated in FIG. 10. A cast upright60 is formed integrally with bulkhead 11 and receives the root portion52. With such an arrangement, the crash rails 20, 30, 40, 50 could beused to provide the main support for the whole front end of a motorvehicle, i.e. forming the main connection between the front end (frontwings, bonnet, front suspension, front sub-frame, engine) and theremainder of the vehicle.

The front tips 21, 31, 41, 51 of the crash rails 20, 30, 40, 50 could beflanged to assist the attachment of the front tips 21, 31, 41, 51 to abumper.

Whilst above the crash rails 20, 30, 40, 50 have been described ashaving cavities of closed cross-section, and this is advantageous fortorsional rigidity, a crash rail could be formed from a corrugated sheetwith a groove or grooves open to one side, provided that thecross-sectional area(s) of the groove(s) taper(s) in accordance with thepresent invention and the wall thickness(es) of the corrugated sheetalso taper(s).

It will be appreciated that whilst the crash rail according to thepresent invention has been described for use as a crash structure infront of a passenger cell of a vehicle, the crash rails 20, 30, 40, 50described above are equally suitable for use in providing a crashstructure at the rear of a passenger cell.

What is claimed is:
 1. A crash rail for a vehicle comprising: a rootportion which can be anchored to a part of the vehicle; a tip portionwhich is spaced apart from the root portion and which is located nearera potential impact point of the vehicle when the root portion isanchored to the said part of the vehicle; and a middle portion whichextends from the root portion to the tip portion; wherein: the crashrail comprises a wall which defines a groove or a cavity in the crashrail; the groove or the cavity in the crash rail has a cross-sectionalarea which increases gradually from the tip portion to the root portion;the wall has a thickness which increases gradually from the tip portionto the root portion; the wall is composed of a composite material havingfibres set in a resin material; the crash rail can be crushed when thevehicle impacts with another object to thereby absorb energy of theimpact; during the impact the crash rail disintegrates with the resinseparating from the fibres set therein; and during the impact the crashrail disintegrates progressively with the tip portion disintegratingfirst and then the middle portion and lastly the root portion.
 2. Acrash rail as claimed in claim 1 wherein the wall comprises longitudinalfibres which extend along the wall from the root portion towards the tipportion.
 3. A crash rail as claimed in claim 2 wherein all of thelongitudinal fibres extend from the root portion, the longitudinalfibres being arranged in bundles of different lengths, some of thefibres extending to the tip portion and the rest being of graduatedlength so as to stop short of the tip portion.
 4. A crash rail asclaimed in claim 3 wherein each bundle of longitudinal fibres isarranged so that each fibre lies side by side to form a lamina ofdefined length and each bundle forms a separate lamina of differentlength.
 5. A crash rail as claimed in claim 2 wherein the wall comprisesadditionally multidirectional fibres distributed along the length of thecrash rail.
 6. A crash rail as claimed in claim 5 wherein themultidirectional fibres are present in a mat set in the resin material.7. A crash rail as claimed in claim 5 wherein the multidirectionalfibres are provided near the surface of the wall of the crash rail.
 8. Acrash rail as claimed in claim 5 wherein at the tip portion of the crashrail the percentage of the wall which comprises the multidirectionalfibres is greater than the percentage of the wall comprising themultidirectional fibres at the root portion.
 9. A crash rail as claimedin claim 5 wherein at the root portion of the crash rail the percentageof the wall which comprises longitudinal fibres is greater than thepercentage of the wall comprising the longitudinal fibres at the tipportion.
 10. A crash rail as claimed in claim 1 which is formed as asingle piece hollow moulding with a cavity extending therethrough.
 11. Acrash rail as claimed in claim 10 wherein the cavity is of generallysquare cross-section.
 12. A crash rail as claimed in claim 10 whereinthe cavity is of generally rectangular cross-section.
 13. A crash railas claimed in claim 10 wherein the cavity is of generally circularcross-section.
 14. A crash rail as claimed in claim 1 comprising twomoulded portions each having a groove, whereby when the moulded portionsare joined together the grooves in the moulded portions co-operatetogether to define a cavity extending along the crash rail.
 15. A crashrail as claimed in claim 14 wherein the grooves are each U-shaped andtogether define a square cross-section cavity.
 16. A crash rail asclaimed in claim 14 wherein the grooves are each U-shaped and togetherdefine a rectangular cross-section cavity.
 17. A crash rail as claimedin claim 14 wherein the grooves are each of semi-circular section andtogether define a circular cross-section cavity.
 18. A crash rail asclaimed in claim 14 wherein each moulded portion has two flangesadjacent the groove therein and the flanges of the moulded portions areadhered together to join the moulded portions.
 19. A crash rail asclaimed in claim 1 comprising two corrugated moulded portions eachhaving a pair of parallel spaced apart grooves which when the mouldedportions are joined together form a pair of parallel extending cavities.20. A crash rail as claimed in claim 19 wherein the pair of grooves areboth U-shaped and together define square cross-section cavities.
 21. Acrash rail as claimed in claim 19 wherein the pair of grooves are bothU-shaped and together define rectangular cross-section cavities.
 22. Acrash rail as claimed in claim 19 wherein the pair of grooves are bothof semi-circular section and together define circular section cavities.23. A crash rail as claimed in claim 19 wherein the moulded portionseach have flanges moulded adjacent the grooves therein and each flangeof one moulded portion is adhered to a facing flange of the othermoulded portion to join the moulded portions.
 24. A crash rail asclaimed in claim 1 comprising a corrugated moulded portion having agroove and a panel joined to the moulded portion, the panel having agenerally flat surface which defines with the groove a cavity extendingalong the crash rail.
 25. A crash rail as claimed in claim 24 whereinthe groove is U-shaped and defines with the generally flat surface asquare cross-section cavity.
 26. A crash rail as claimed in claim 24wherein the groove is U-shaped and defines with the generally flatsurface a rectangular cross-section cavity.
 27. A crash rail as claimedin claim 24 wherein the groove is semi-circular and defines with thegenerally flat surface a semi-circular cross-section cavity.
 28. A crashrail as claimed in claim 1 comprising a moulded portion having a pair ofparallel extending grooves and a panel joined to the moulded portion,wherein the panel has a generally flat surface which defines with thegrooves a pair of spaced apart cavities extending along the crash rail.29. A crash rail as claimed in claim 28 wherein the grooves are U-shapedand define with the generally flat surface square cross-sectioncavities.
 30. A crash rail as claimed in claim 28 wherein the groovesare U-shaped and define with the generally flat surface rectangularcross-section cavities.
 31. A crash rail as claimed in claim 28 whereinthe grooves are semi-circular and define with the generally flat surfacesemi-circular cross-section cavities.
 32. A crash rail as claimed inclaim 24 wherein the panel is adhered to the moulded portion by anadhesive which permits the panel to peel away from the moulded portionas the moulded portion disintegrates during impact.
 33. A crash rail asclaimed in claim 32 wherein the moulded portion has flanges to which thegenerally flat surface of the panel is adhered to join the mouldedportion to the panel.
 34. A crash rail as claimed in claim 33 whereinthe generally flat surface-is slightly corrugated at least in thoseregions of the panel which are adhered to the flanges, the corrugationsin the generally flat surfaces leaving areas where the adhesive does notinterconnect the flanges and such areas acting to impede the spread ofcracks through the adhesive.
 35. A wheeled motor vehicle having apassenger cabin and a bumper located forward of the passenger cabin anda crash rail as claimed in claim 1 interconnecting the passenger cabinand the bumper.
 36. A wheeled motor vehicle having a passenger cabin anda bumper located forward of the passenger cabins and a plurality crashrails each as claimed in claim 1, each crash rail being spaced apartfrom the other crash rails and each crash rail interconnecting thepassenger cabin and the bumper.
 37. A wheeled motor vehicle having apassenger cabin, an engine in an engine bay located forward of thepassenger cabin, a bumper located forward of the engine bay and a pairof crash rails each as claimed in claim 1 interconnecting the passengercabin and the bumper in spaced part configuration with one on eitherside of the engine bay.
 38. A wheeled motor vehicle having a passengercabin, an engine in an engine bay located forward of the passengercabin, a bumper located forward of the engine bay and a pair of crashrails each as claimed in claim 24 wherein the panel of each crash railhas a surface which provides a liner surface for the engine bay.
 39. Awheeled motor vehicle having a passenger cabin and a bumper located tothe rear of the passenger cabin and a crash rail as claimed in claim 1interconnecting the passenger cabin (10) and the bumper.
 40. A wheeledmotor vehicle having a passenger cabin and a bumper located to the rearof the passenger cabin (10) and a plurality crash rails each as claimedin claim 1, each rail being spaced apart and interconnecting thepassenger cabin and the bumper.
 41. A wheeled motor vehicle having apassenger cabin, an engine in an engine bay located to the rear of thepassenger cabin, a bumper located to the rear of the engine bay and apair of crash rails each as claimed in claim 1 interconnecting thepassenger cabin and the bumper in spaced apart configuration with one oneither side of the engine.
 42. A wheeled motor vehicle having apassenger cabin, an engine in an engine bay located to the rear of thepassenger cabin, a bumper located to the rear of the engine bay and apair of crash rails each as claimed in claim 24 wherein the panel ofeach crash rail has a surface which provides a liner surface for theengine bay.
 43. A wheeled motor vehicle as claimed in claim 35 whereinthe crash rail or rails are connected to the passenger cabin by slottingthe end or ends of the rail or rails into matching slots in uprightsattached to the passenger cabin.